Fatty acids are important components of lipids such as phospholipids and triacylglycerols. Various physiological activities have been reported for polyunsaturated fatty acids (PUFA) containing two or more unsaturated bonds, including arachidonic acid, dihomo-γ-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid (Non-patent Document 1). These polyunsaturated fatty acids are expected to have applications in various fields. To efficiently obtain these fatty acids, microbial techniques have been developed which involve culturing various microorganisms to obtain polyunsaturated fatty acids. Other attempts have also been made to produce polyunsaturated fatty acids in plants. In these cases, polyunsaturated fatty acids are known to be accumulated, for example, as components of storage lipids such as triacylglycerols within microorganism cells or plant seeds.
This triacylglycerol is produced in vivo starting from glycerol-3-phosphate via lysophosphatidic acid, phosphatidic acid and diacylglycerol.
As described above, the reaction in which lysophosphatidic acid (hereinafter also referred to as “LPA” or “1-acylglycerol-3-phosphate”) is acylated to generate phosphatidic acid (hereinafter also referred to as “PA” or “1,2-diacyl-sn-glycerol-3-phosphate”) is known to be mediated by lysophosphatidic acid acyltransferase (hereinafter also referred to as “LPAAT”).
This LPAAT is also known as 1-acylglycerol-3-phosphate acyltransferase (E.C. 2.3.1.51). LPAAT genes have been reported so far in several organisms. As an LPAAT gene from Escherichia coli, the plsC gene has been cloned (Non-patent Document 2). In fungi, the SLC1 gene from Saccharomyces cerevisiae has been cloned (Non-patent Document 3). Likewise, LPAAT genes have also been cloned from animals and plants (Patent Document 1).
For the LPAAT gene from a lipid-producing fungus, Mortierella alpina (hereinafter also referred to as “M. alpina”), two homologs have been reported (Patent Documents 2 and 3).
Patent Document 2 discloses cloning of a M. alpine-derived LPAAT homolog (LPAAT1), which is a gene having a CDS of 1254 nucleotides and consisting of the nucleotide sequence shown in SEQ ID NO: 16. This document also reports that when this LPAAT1 was co-expressed in yeast cells with Δ6 desaturase and Δ6 elongase and cultured in a medium supplemented with specific fatty acids, such yeast cells produced larger amounts of fatty acids whose chain length is longer and/or whose unsaturation degree is higher than that of the supplemented fatty acids, when compared to strains not expressing LPAAT1 (Patent Document 2).    Patent Document 1: International Patent Publication No. WO2004/076617    Patent Document 2: US Patent Publication No. 2006/174376    Patent Document 3: US Patent Publication No. 2006/0094090    Non-patent Document 1: Lipids, 39, 1147 (2004)    Non-patent Document 2: Mol. Gen. Genet., 232, 295-303, 1992    Non-patent Document 3: J.B.C., 268, 22156-22163, 1993    Non-patent Document 4: Biochemical Society Transactions, 28, 707-709, 2000    Non-patent Document 5: J. Bacteriology, 180, 1425-1430, 1998    Non-patent Document 6: J. Bacteriology, 173, 2026-2034 1991